ULTRAMAFIC XENOLITHS FROM ADAGDAK VOLCANO, ADAK, ALEUTIAN-ISLANDS, ALASKA - DEFORMED IGNEOUS CUMULATES FROM THE MOHO OF AN ISLAND-ARC
ULTRAMAFIC XENOLITHS FROM ADAGDAK VOLCANO, ADAK, ALEUTIAN-ISLANDS, ALASKA - DEFORMED IGNEOUS CUMULATES FROM THE MOHO OF AN ISLAND-ARC
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DOI：
10.1086/629133
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发表时间：
1987-05-01
影响因子：
1.8
通讯作者：
KAY, RW
中科院分区：
文献类型：
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作者：
DEBARI, S;KAY, SM;KAY, RW
阿留申岛弧中部阿达克岛上阿达达克火山冰后期喷出物存款中发现了变形超镁铁质捕虏体和玄武岩残留物。这些纯橄榄岩，韦氏岩，单斜辉石，斜长角闪岩被解释为堆积从原始弧岩浆形成的岩浆房下的壳幔边界。原始弧岩浆的成分与捕虏体的寄主玄武岩（11.8%MgO）相似。微量元素和Nd、Sr同位素数据表明，这些捕虏体与阿留申钙碱性火山岩来自同一母岩。橄榄岩捕虏体中含有橄榄石（F_（086.6）~ 83.2）、单斜辉石（FS_（4.1）En_（46.4）WO_（49.5）~ FE_（5.2）En_（46.6）WO_（48.2））、铬铝尖晶石（19- 30%和30-42%）和次生分凝角闪石（FeO含量随单斜辉石含量的增加而增加）。这些捕虏体形成必要的残留物，以产生高铝玄武岩预测在一个开放系统的混合模型阿留申钙碱性火山作用。橄榄岩的重结晶结构，沿着具有高平衡温度（> 1000°C），表明上地幔软流圈流动状态到达壳幔边界区。
Deformed ultramafic xenoliths with basaltic salvages occur in a postglacial ejecta deposit from Adagdak volcano on Adak Island in the central Aleutian Island Arc. These dunites, wehrlites, clinopyroxenites, and amphibolites are interpreted to be cumulates from primitive arc magmas that formed in magma chambers beneath the crust-mantle boundary. The primitive arc magmas are similar in composition to the xenolith's host basalt (11.8% MgO). Trace element and Nd and Sr isotopic data are consistent with derivation of these xenoliths from the same parent as other Aleutian calc-alkaline volcanic rocks. The peridotite xenoliths contain olivine (F086.6 to 83.2), clinopyroxene (FS4.1En46.4Wo49.5 to FE5.2En46.6Wo48.2), Cr-Al spinel (19-30%and 30-42%), and secondary pargasitic amphibole that increase in FeO content as the percentage of clinopyroxene increases. These xenoliths form the necessary residuum to produce the high-Al basalt predicted in an open system mixing model for Aleutian calc-alkaline volcanism. The recrystallized textures of the peridotites, along with high equilibration temperatures (> 1000°C), suggest that the upper mantle asthenospheric flow regime reaches the crust-mantle boundary region.